usb/isp1760: Handle toggle bit in queue heads only

Remove redundant "toggle" member from struct isp1760_qtd, and store toggle
status in struct isp1760_qh only.

Signed-off-by: Arvid Brodin <arvid.brodin@enea.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>